Discussion.—Punctaconchus differs from serpulid and spi− rorbid polychaetes in its microlamellar shell structure, the presence of numerous small pores (punctae) in the tube wall and the closed origin of the tube. The new genus resembles the type species of the Microconchida, Microconchus carbo− narius Murchison, 1839, in its size, spirally coiled tube, microlamellar structure and punctae. However, it differs in having much larger punctae and an internal surface orna− mented by a pattern of ridges resembling ripplemarks. Pun− ctaconchus tubes also increase in diameter more rapidly than those of Microconchus and the inner whorls are more exten− sively overlapped by the outer whorls.

The only punctate Mesozoic microconchid hitherto de− scribed is Pseudobrachidium germanicum Grupe, 1907 from the Late Triassic of Germany (Warth 1982). It differs from the new genus in having much smaller pores, and in this respect resembles Microconchus. Unlike Punctaconchus, tubes of Pseudobrachidium can become uncoiled during late growth stages, as in some Microconchus. Indeed, it is possible that Pseudobrachidium is a junior synonym of Microconchus. The new genus resembles Palaeoconchus Vinn, 2006, and Annuliconchus Vinn, 2006, both from the early Palaeozoic of Baltoscandia. However, both of these genera lack punctae and Annuliconchus also has an annulated tube. Neither Palaeo− conchus nor Annuliconchus has the distinctive, ripplemark− like tube interiors characteristic of Punctaconchus. Spirorbis midfordensis Richardson, 1907 is reassigned to Punctaconchus because of its microlamellar shell structure characteristic of microconchids, the presence of large punctae penetrating the tube wall at regular intervals and the ripple− mark−like ornament of the tube interior.

The three species of Punctaconchus (P. ampliporus, P. midfordensis, and P. palmeri) can be distinguished using the characters of external ornamentation and porosity. P. ampli− porus has relatively smooth tubes with large, dense punctae, P. midfordensis has tubes with sharp longitudinal striations, and P. palmeri tubes have oblique ornamentation in early on− togeny and sparse punctae.

Stratigraphic and geographic range.—Middle Jurassic, Late Aalenian to Late Bathonian of England, and Normandy, France; also questionably occurring in the Early Jurassic, Toarcian of England.

Punctaconchus ampliporus sp.nov.

Figs. 1, 2.

Derivation of the name: In reference to the large (Latin amplus) pores (Latin pori).

Discussion.—This new species resembles Punctaconchus midfordensis in the size of the tubes and presence of large punctae in the tube walls. However, it differs in having a smooth tube exterior and slightly fainter ridges on the tube interior, as well as more densely packed punctae. The very dense porosity of the tubes of P. ampliporus is particularly evident in a specimen (Fig. 2E) in which the punctae have been cast naturally by diagenetic minerals. Whereas the microlamellar tube of the new species appears to be com− posed of calcite platelets or laths, that of P. midfordensis is fi− brous (Fig. 3C), although this apparent difference may be diagenetic.

In his description of Spirorbis midfordensis, Richardson (1907) mentioned being shown a specimen of the brachiopod Pseudoglossothyris simplex from the Pea Grit (Upper Aale− nian) encrusted by numerous Spirorbis. These are likely to have been Punctaconcus ampliporus which is represented at this stratigraphical level in the NHM collections.

Remarks.—Punctaconchus midfordensis resembles the Trias− sic species Microconchus phlyctaena Brönnimann and Zani− netti, 1972, but differs in having strongly developed longitudi− nal ridges and large punctae. All known specimens of this spe− cies are detached from their substrates, unlike the other two species of Punctaconchus in which all specimens are pre− served firmly cemented to hard substrates. The identity of the substrates used by P. midfordensis is unknown. Possibilities include plants or soft bodied animals, or alternativelymolluscs with aragonitic shells which are typically lost through leaching in these Middle Jurassic carbonates.

1981 Spirorbula sp.; Palmer and Fürsich 1981: 7, pl. 2: 12. Derivation of the name: After Timothy J. Palmer who, along with Franz T Fürsich, described the palaeoecology of the sponge reefs in which the new species is found.

Discussion.—Punctaconchus palmeri is similar to both P. ampliporus and P. midfordensis in having punctate tube walls and a ripplemark−like ornament on the interior surface of the tube. It resembles P. ampliporus in lacking prominent longitudinal ridges on tube exteriors, but differs in having sparser and much smaller pores and a stronger ripplemark− like ornament on the tube interior. It also differs in showing a more rapid increase in tube diameter. Punctaconchus pal− meri differs from P. midfordensis in lacking prominent lon− gitudinal ridges, and in having sparser and much smaller punctae.

This species was assigned by Palmer and Fürsich (1981) to the genus Spirorbula Nielsen, 1931. The original material of Spirorbula comes from the Danian of Denmark and com− prises two species, S. cingulata Nielsen, 1931, and S. tortilis Nielsen, 1931, which are either spirorbids or coiled ser− pulids. They are unrelated to microconchids.